1. Field of the Invention
This invention relates to the reduction of weight in automotive vehicles, and, more particularly, to a door assembly utilizing magnesium to reduce weight and increase fuel economy.
2. Background of the Invention
During the last decade, manufacturers of automobiles have undertaken steps to reduce weight of the vehicles in order to improve fuel economy and to reduce vehicle emissions. Such efforts have included the design of automotive vehicle components utilizing light metal alloys, leading to a variety of applications in chassis and power train components. More recently, advances in high-pressure die-casting technologies have enabled these technologies to be applied to larger structural components. Noteworthy examples of such larger components are instrument panel reinforcements, seat frames and door closure panels. While weight reductions of 40% can be realized through the use of magnesium, product engineers are faced with new challenges to incorporate adequate stiffness and crash critical applications with a material system possessing lower modulus and ductility compared to conventional formed sheet metal construction of such components.
Increasing the numbers of materials to be utilized in the construction of large structural components for automotive vehicles requires alternative joining strategies for the disparate materials in the assembly of such structural components. Consideration must be given to galvanic corrosion, as well as to differences in thermal expansion rates. Other related issues include the integration of the new materials and assembly techniques into the existing framework of an automotive manufacturing and assembly plant.
In U.S. Pat. No. 5,536,060, issued to Moinuddin Rashid, et al. on Jul. 16, 1996, an automotive door assembly is disclosed in which a reinforcement panel is attached to the interior side of the outer panel of the door assembly. This reinforcement panel is described as having superplastic forming qualities such as aluminum and stainless steel, but acknowledges that magnesium can be employed optionally, to provide the complex shape required in the specific reinforcement panel designed for the disclosed application.
In U.S. Pat. No. 4,662,115, issued to Takegi Ohya, et al. on May 5, 1987, an automotive vehicle door assembly is disclosed incorporating the employment of an inner panel formed of steel and an outer panel formed of synthetic resin. The hinge and door closure and locking devices are mounted on the steel inner panel.
U.S. Pat. No. 5,924,760, was issued to Paul Krajewski, et al. for a one piece corrugated anti-intrusion barrier for an automotive vehicle door. This anti-intrusion barrier is preferably formed in a corrugated configuration from a piece of sheet metal stamped into the preferred form. These barrier panels are preferably formed from aluminum alloys, though other materials including magnesium, steel, and titanium can be alternatively utilized.
U.S. Pat. No. 5,944,373, issued to Dinesh Seksaria on Aug. 31, 1999, is directed to a lightweight tailgate assembly for a pick-up truck in which a plastic reinforcing member is positioned between two metal panels to form the completed tailgate assembly. The inner and outer tailgate panels may be formed of aluminum or magnesium to minimize weight considerations.
In U.S. Pat. No. 6,068,327, issued to Michael Junginger on May 30, 2000, an upwardly folding rear cargo door for an automotive vehicle is disclosed. Junginger indicates that magnesium would be material preferred over aluminum, steel and plastic because of the reduction in weight of the assembly without the loss of strength. Junginger, however, does not disclose how a composite door structure incorporating magnesium with other structural materials can be effectively combined to create a vehicle door assembly.
U.S. Pat. No. 4,919,473, issued to Johann Laimighofer on Apr. 24, 1990, is directed to a structural beam for incorporation into an automotive vehicle door as an anti-intrusion device. Like the other references noted above, Laimighofer acknowledges that the structural beam may be formed from magnesium, but does not address the issues of how the disparate materials may be properly joined and deployed into a composite vehicle door assembly.
It would, therefore, be desirable to provide a composite automotive vehicle door assembly formed from disparate materials to provide a lightweight door assembly without sacrificing strength and intrusion resistance.